Adobe recently released a new program (named Alchemy) that compiles C/C++ source code for Flash. I've got to say that this is the most exciting thing I've seen come out of Adobe/Macromedia in years. I haven't had time to dig into yet, but my brain is already racing with ideas to explore...libraries I've always wanted to port to ActionScript.
According to Adobe:
We are making this software available to gauge community interest in Alchemy and welcome your feedback. ... Please also note that this is a research project and there is no assurance that there will be a shipping version of Alchemy
So, if you're interested in this program, get busy with it and tell Adobe all about it--what rocks, and what needs more work?
Some resources for getting started: